The present invention relates to a method for diagnosing, monitoring and treating cardiovascular pathologies, and more particularly to a method of determining hemodynamic parameters in a human cardiovascular system by analyzing arterial waveforms, methods for using the parameters so determined for diagnosing hypertension and other cardiovascular problems and diseases, and devices that incorporate the methods of the present invention.
Cardiovascular disease is a leading cause of death and disability. One cardiovascular disease that affects a large number of people is hypertension, which is defined as abnormally elevated blood pressure. Hypertension is quite common. It is estimated that over 60,000,000 Americans suffer from hypertension.
To prevent cardiac disorders from causing death, serious illness and disability, it is important to monitor the condition of a person""s cardiovascular system, and to analyze the data from the monitoring so performed to determine whether any pathologies exist in the person""s cardiovascular system that should be treated to prevent further degradation of the patient""s cardiovascular system.
The method used most often to monitor a cardiovascular condition is the determination of the blood pressure of the patient. Human blood pressure is normally described by systolic and diastolic pressure readings, which are usually given in millimeters of mercury (mmHg). The systolic pressure is the higher of the two values given, and the diastolic pressure is the lower of the two values given. From a physiologic standpoint, the systolic pressure usually represents that pressure at which blood begins flowing through an artery that is compressed by a blood pressure cuff during a blood pressure measurement. At pressures above the systolic pressure (supra-systolic pressures) the flow of blood through the artery is blocked by the blood pressure cuff used to take the blood pressure reading. The diastolic pressure is that pressure below which the blood flow through the artery is unimpeded by the blood pressure cuff. A further explanation of the physiologic basis of the systolic and diastolic blood pressure readings can be found in Chio, U.S. Pat. No. 4,880,013, that issued on Nov. 14, 1989, and Chio U.S. Pat. No. 5,162,991, that issued on Nov. 10, 1992. The Chio ""013 and ""991 patents were invented by the Applicant, and are assigned to the assignee of this application.
It is generally accepted that a systolic blood pressure reading of greater than 140 mmHg, and/or a diastolic blood pressure reading of greater than 90 mmHg is indicative of a hypertensive condition. These pressure readings are generally considered to be indicative of hypertension, regardless of whether these blood pressure readings are made by non-invasive or invasive blood pressure determination methods.
Although systolic blood pressure and diastolic blood pressure readings are useful for determining whether hypertension exists, they are not completely reliable. The systolic/diastolic hypertension threshold (140 mmHg/90 mmHg) line of demarcation does not always provide a completely accurate guide for determining either which patients are hypertensive, or what factors caused the hypertension. In this regard, it is believed that approximately 80% of hypertension cases are categorized as xe2x80x9cessential hypertension.xe2x80x9d A diagnosis of xe2x80x9cessential hypertensionxe2x80x9d usually means that the causes of the hypertension are unknown. As such, these persons having xe2x80x9cessential hypertensionxe2x80x9d may not be diagnosed accurately and reliably by only measuring the patient""s systolic and diastolic pressures. For example, a patient may have a measured systolic and diastolic pressure of less than 140 (systolic)/90 (diastolic), but still may be genetically hypertensive. Conversely, a person may have a measured systolic/diastolic blood pressure of greater than 140/90, but may be not hypertensive either through environment, or genetic causes. Most importantly, it is difficult, if not impossible for a physician to treat a patient""s hypertension properly if the physician does not know the cause of the hypertension.
For more than twenty years, studies have been conducted to find other physiological hemodynamic parameters in addition to systolic and diastolic blood pressure readings. For example, in the mid-1970""s, Watt performed studies that tried to evaluate the xe2x80x9ccompliancexe2x80x9d or xe2x80x9celasticityxe2x80x9d of an artery. Watt, T. B. at et al., Arterial Pressure Contour Analysis for Estimating Human Vascular Properties, J. Applied Physics, (1976); at pages 171-176. In Watt""s study, he used an electrical circuitry model, and a Windkessel model that were modified for a human arterial system to make his model for determining physiological and hemodynamic parameters. Watt""s model defined two compliance components, C1 and C2, a Resistance, R and an Inductance, L. By using equations that had their genesis in the electrical circuitry art area, Watt further defined that C1 was the elastic compliance of major or large arteries. This factor (C1) was also called xe2x80x9cproximal compliance.xe2x80x9d Watt found that C2 is the compliance of the smaller peripheral arteries, which is also referred to as xe2x80x9cdistal compliance.xe2x80x9d
Watt reported that correlations existed between the value of the proximal compliance (C1) and the distal compliance (C2) and the existence of hypertension. Primarily, Watt found that hypertensive patients tended to have smaller compliance values (C1 and C2). Since Watt""s study, many other studies have been conducted that were focused on the arterial compliances and their relations to various causes of hypertension. Many groups have reported the relationship between proximal compliance (C1) and hypertension. In U.S. Pat. No. 5,054,493, which issued Oct. 8, 1991, J. N. Cohn, et al. reported his findings that distal compliance (C2) is more sensitive than proximal compliance (C1) for determining hypertension. Cohn therefore suggested that distal compliance (C2) was a better parameter for diagnosing hypertension than proximal compliance (C1). Cohn is also worth reviewing for its discussion of the Windkessel model, and its citation of a large number of references dealing with studies relating to compliance. At column 3, Cohn cites a larger number of studies conducted on the properties of the large proximal arteries, and the relationship of the properties of these arteries (in particular their compliance (C1)) to hypertension.
Since C2 is the distal compliance, and since distal compliance is strongly influenced by the reflection wave from the peripheral arteries in the arterial system, its measurement may need to be performed either by an invasive method, or alternately by a very sensitive non-invasive sensing device. An extremely sensitive non-invasive sensing device is probably necessary in order to obtain a near-perfect wave of the type that is typically found when using invasive techniques. This reflection phenomenon and its impact on its measurement was reported by Schwid, in Schwid, H. A., et al., Computer Model Analysis of Radial Artery Pressure Waveforms, J. Clinical Monitoring (1987), Vol. 3, No. 4, at pages 220-228. Additionally, the measurement of distal compliance (C2) may also be affected by the reflection wave. Further, the measurement of distal compliance may have fluctuations caused by other human factors, such as fluctuations in the arterial cross-section area and arterial blockage at the measured limb. As such, distal compliance C2 is still not a very reliable parameter for determining the physical conditions of a human cardiovascular system and other hemodynamic parameters. A recent study by Hayoz suggests that compliance may not be a valid indicia of hypertension, as Hayoz""s study found that the elastic behavior (compliance) was not necessarily altered by an increase in blood pressure. See, Hayoz, D. et al., Conduit Artery Compliance and Distensibility are Not Necessarily Reduced in Hypertension, Hypertension 1992, Vol. 20, at pages 1-6.
Although the references cited above all relate to methods for determining cardiac and cardiovascular condition, and some of the methods discussed above relate to hemodynamic parameters other than the determination of systolic and diastolic pressure, room for improvement exists.
It is therefore one object of the present invention to provide an improved method for determining hemodynamic parameters in a human cardiovascular system.
In accordance with the present invention, a method is provided for diagnosing a cardiovascular pathology in a patient. The method comprises the steps of (1) gathering cardiovascular condition information from the patient, and (2) determining the patient""s systolic, diastolic and mean arterial pressures from the gathered cardiovascular condition information. At least one of the determined diastolic, systolic and mean arterial pressures is used to determine the patient""s peripheral resistance. The determined peripheral resistance is then compared to a predetermined peripheral resistance threshold value. The patient is then diagnosed as having a cardiovascular pathology if the patient""s determined peripheral resistance exceeds the predetermined peripheral resistance threshold value.
In a preferred embodiment of the present invention, the method further comprises the steps of using at least one of the determined diastolic, systolic and mean arterial pressures to determine the patient""s cardiac output. The determined cardiac output is then compared to a predetermined threshold value. The patient is diagnosed as hypertensive if the product of the patient""s cardiac output and peripheral resistance exceeds the predetermined threshold value. Preferably, the predetermined threshold value against which the determined product of cardiac output and peripheral resistance is compared is a predetermined mean arterial pressure threshold value, i.e. MAP=(CO)(PR).
Also in accordance with the present invention, a method is provided for diagnosing a patient as being at risk for having a cardiovascular pathology. This method comprises the steps of affixing a non-invasive pressure inducing means and transducer means to a patient. The pressure induced by the pressure inducing means is elevated to a supra-systolic pressure, and is then decreased over time to a sub-diastolic pressure. A data stream is obtained from the transducer means. The data stream includes pressure data and pulsation signal data, to obtain a series of pulsation signal data waveforms. The waveforms include at least pulsation signal data taken at a supra-systolic pressure, and pulsation signal data taken at a sub-diastolic pressure. A pseudo-aortic wave contour is created from the obtained supra-systolic waveform data and the sub-diastolic waveform data. The patient is then diagnosed as having a cardiovascular pathology by comparing the pseudo-aortic wave contour to cardiovascular contours exhibiting known cardiovascular pathologies.
Further in accordance with the present invention, a method is provided for diagnosing a patient as being at risk for having a cardiovascular pathology. This method comprises the steps of affixing a non-invasive pressure inducing means and transducer means to the patient. The pressure induced by the pressure inducing means is then elevated to a supra-systolic pressure. The pressure induced by the pressure inducing means is then decreased over time to sub-diastolic pressure. A data stream is obtained from the transducer means. The data stream includes pressure data and pulsation signal data, to obtain a series of pulsation signal data waveforms. The waveforms include at least pulsation signal data taken at a supra-systolic pressure, and pulsation signal data taken at a sub-diastolic pressure. The peak cardiac contractility is then determined from the data stream so obtained. The patient can then be diagnosed as having a cardiovascular pathology based on the determined peak cardiac contractility.
Additionally, in accordance with the invention, methods are disclosed for determining peripheral resistance, diastolic flow velocity, left ventricle contractility, and the compliance of the artery. Further, the invention comprises an apparatus for determining these parameters.
One feature of the present invention is that a wide range of hemodynamic parameters can be determined through non-invasive means. Many of the parameters discovered by the Applicant, and disclosed in connection with this invention were not heretofore either obtainable, or recognized as being useful for diagnosing cardiovascular pathologies. Further, some of the parameters of the present invention were formerly obtainable only through an invasive procedure that usually involved catheterizing the patient. The Applicant""s invention improves upon these prior invasive techniques, by enabling the practitioner to have access to a greater array of data without requiring the patient to go through the discomfort and expense associated with invasive procedures.
A further feature of the present invention is that it provides a method for analyzing arterial pulse waveforms which can be measured from non-invasive cuff pulse waves to derive hemodynamic parameters, such as diastolic flow velocity, peripheral resistance, compliance, or elastic constant of an artery, and cardiac (left ventricle (LV)) contractility.
Another feature of the present invention is that the applicant has found that the peripheral resistance derived from the diastolic flow velocity is a better method for diagnosing hypertension than using compliance. The cardiac (LV) contractility obtained by the applicants"" technique of using non-invasive means is useful for determining not only hypertension, but certain other cardiac problems and irregularities.
These and other features will become apparent to those skilled in the art upon a review of the detailed description of a preferred embodiment of the present invention presented below, in conjunction with the drawings presented herewith.